System and method for in-sea electrode conditioning

ABSTRACT

Disclosed are methods and systems for conditioning electrodes while deployed in the sea with a marine electromagnetic survey system. An embodiment of the method may comprise deploying electrodes in seawater during a marine electromagnetic survey. The method further may comprise coupling at least one of the electrodes to a controllable current/voltage source while the electrodes are deployed in the seawater. The method further may comprise sending a first conditioning signal from the controllable current/voltage source to the at least one of the electrodes coupled to the controllable current/voltage source.

BACKGROUND

The present invention relates generally to the field of marineelectromagnetic surveying. More particularly, in one or moreembodiments, this invention relates to methods and systems forconditioning electrodes while deployed in the sea, for example, with amarine electromagnetic survey system.

One technique for marine electromagnetic surveying involves towing anenergy source at a selected depth in a body of water. One or more surveycables also may be towed in the water at selected depths. The surveycables are essentially long cables having electromagnetic sensorsdisposed thereon at spaced apart locations. The energy source and surveycables may be positioned in the water by attached equipment, such asdeflectors and position control devices. Actuation of the energy sourceemits an energy field into the body of water. The energy field interactswith the rock formations below the water bottom. The change in theenergy field due to the interaction with the subterranean rock formationis detected by the electromagnetic sensors and used to infer certainproperties of the subsurface rock, such as structure, mineralcomposition and fluid content, thereby providing information useful inthe recovery of hydrocarbons. In addition to towed survey cables,electromagnetic survey systems may also use sensors that are at a fixedlocation with respect to the energy source, which may include attachmentof electromagnetic sensors on one or more cables positioned on the waterbottom or attachment of the electromagnetic sensors to one or subsurfaceacquisition nodes, for example.

Electrodes may be used in one or more of the components that are used inelectromagnetic survey systems. For example, electromagnetic sources andelectromagnetic sensors may each include a pair of electrodes. Whendeployed for an electromagnetic survey, these electrodes can be exposedto seawater, which may undesirably interact with the surface of theelectrodes. For example, because a potential difference is typicallyapplied across the electrodes during use, the surface of the electrodescan react with the seawater causing undesirable deposits that candegrade electrode performance. In addition, electrode performance canalso be degraded by algae and other biological contaminations or growthsthat may occur on the surface of the electrodes. In some instances, thedegradation of electrode performance caused by these undesirableinteractions can limit the operational life of the electrodes used inthe marine electromagnetic survey systems, as the interactions mayresult in decreased accuracy of measurements from sensor electrodes, forexample. The current technique for restoring performance to theelectrodes when these undesirable interactions have undesirably degradedtheir performance is to retrieve the electrodes and install replacementelectrodes above the surface of the water. Drawbacks to this techniquefor restoring performance include the undesirable impact on theoperational efficiency and safety of the survey systems caused by thetime, effort, and expense associated with retrieval and replacement ofthe electrodes.

Accordingly, there is a need for improved methods and systems forrestoration of electrode performance in marine electromagnetic surveysystems.

BRIEF DESCRIPTION OF THE DRAWINGS

These drawings illustrate certain aspects of some of the embodiments ofthe present invention and should not be used to limit or define theinvention.

FIG. 1 is a schematic view of an electrode conditioning system inaccordance with embodiments of the present invention.

FIG. 2 is a schematic view of an electrode conditioning system inaccordance with alternative embodiments of the present invention.

FIG. 3 is a schematic view of an electromagnetic survey systemcomprising towed survey cables on which an electrode conditioning systemis installed in accordance with embodiments of the present invention.

FIG. 4 is a schematic view of an electromagnetic survey systemcomprising subsurface acquisition nodes on which electrode conditioningsystems have been installed in accordance with embodiments of thepresent invention.

FIG. 5 is a schematic view of an electromagnetic survey systemcomprising ocean bottom cables on which electrode conditioning systemshave been installed in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

The present invention relates generally to the field of marineelectromagnetic surveying. More particularly, in one or moreembodiments, this invention relates to methods and systems forconditioning electrodes while deployed in the sea with a marineelectromagnetic survey system.

One of the many potential advantages of the systems and methods of thepresent invention, only some of which are disclosed herein, is thatelectrodes may be conditioned while in the sea, thus restoring electrodeperformance without requiring out-of-water retrieval and replacement ofthe electrodes. For example, embodiments of the present invention may beused to condition silver/silver chloride (Ag/AgCl) based electrodes,which are commonly used in electromagnetic survey systems. Becauseseawater contains large amounts of chloride ions, interactions betweenthe surface of the Ag/AgCl-based electrodes and the seawater can becontrolled to restore electrode performance. For example, embodiments ofthe present invention may cause formation of one or more fresh AgCllayers on the surface of the electrode by an electrochemical reaction ofthe Ag from the electrode with chloride ions in the seawater. By way offurther example, embodiments of the present invention may cause removalof an exposed AgCl layer from the surface of the electrode, thusrevealing a fresh AgCl layer while removing undesirable deposits orother contaminants (e.g., algae and other biological contaminants) thatmay have built up on the exposed AgCl layer. Because the electrodes areconditioned while in the sea, operational efficiency and safety of themarine electromagnetic survey system may benefit, as the time, effort,and expense associated with electrode replacement can be reduced, orpotentially even eliminated.

Yet another potential advantage of the systems and methods of thepresent invention is that electrodes may be conditioned while deployedin the sea to create a desired layer on the surface of the electrodes.For example, embodiments of the present invention may be used to createAg/AgCl-based electrodes. In some embodiments, interactions between thesurface of an Ag-based electrode and the seawater can be controlled toform one or more AgCl layers on the surface of the electrode. Becausethe electrodes are created in the sea, the complexity associated withforming Ag/AgCl-based electrodes can be reduced.

FIG. 1 illustrates an electrode conditioning system 5 in accordance withembodiments of the present invention. In the illustrated embodiment, theelectrode conditioning system 5 includes electrodes 10 a and 10 b,counter electrodes 15 a and 15 b, switch 20, and a controllablecurrent/voltage source 25. As illustrated, the electrodes 10 a and 10 bmay be coupled to the switch 20 by lines 30 while the counter electrodes15 a and 15 b may be coupled to the switch 20 by lines 35, and thecontrollable current/voltage source 25 may be coupled to the switch 20by line 40. The switch 20 may also be coupled to electronics 45 by line50. The electronics 45 may include, for example, an amplifier, telemetrysystem, and/or other suitable electronics for operation of theelectrodes 10 a and 10 b.

The electrodes 10 a and 10 b may be any electrode suitable for use inmarine electromagnetic survey systems in accordance with embodiments ofthe present invention. Examples of suitable electrodes include sourceelectrodes and sensor electrodes, such as those used in seismic andelectromagnetic survey systems. In one embodiment, the electrodes 10 aand 10 b are Ag/AgCl-based electrodes, such as those used for sensorelectrodes in electromagnetic survey systems. Those of ordinary skill inthe art will appreciate that Ag/AgCl-based electrodes may be fabricated,for example, from sintering of AgCl onto an Ag rod or by chemically orelectrochemically treating an Ag surface, for example. In the case ofelectrochemically treating the surface, the AgCl surface of theelectrode may be created by an electrochemical reaction of Ag from theelectrode metal with chloride ions in an electrolyte. While a specialsolution is typically formulated that contains the chloride ions for theelectrochemical treatment, the electrodes 10 a and 10 b used in a marineelectromagnetic survey system typically may be deployed in seawater,which contains a large amount of chloride ions in accordance withembodiments of the present invention. As will be discussed in moredetail below, the electrode conditioning system 5 may be used, forexample, to facilitate interactions between the electrodes and theseawater to either form fresh AgCl on, or remove AgCl from, theelectrodes 10 a and 10 b. For example, a fresh layer of AgCl may beformed on an AgCl electrode to yield an Ag/AgCl-based electrode.Alternatively, the AgCl may be formed/removed to recondition anAg/AgCl-based electrode. While the preceding description describes theuse of Ag as the conducting material in the electrodes 10 a and 10 b,the electrical conductor in the electrode may be any appropriateconducting materials, including graphite and other suitable metals, suchas carbon, platinum, and gold, for example.

The counter electrodes 15 a and 15 b may be any electrode suitable forforming an electrode pair with one of the electrodes 10 a and 10 b. Forexample, the counter electrodes 15 a and 15 b may be an appropriatemetal that can interact with the seawater upon application of aconditioning signal, such that metal chloride may be formed on thesurface thereof. In some embodiments, the counter electrode may includeany appropriate conducting material, including graphite and metals, suchas carbon, Ag, platinum, and gold, for example. Although embodimentsshown in FIG. 1 show two counter electrodes 15 a and 15 b, it is to beunderstood that the number of such counter electrodes 15 a and 15 b isnot a limitation on the scope of the invention. Other configurations mayinclude more or fewer counter electrodes 15 a and 15 b. For example, theelectrode conditioning system 5 may include only one counter electrode15 a or 15 b, in some embodiments.

In accordance with present embodiments, the switch 20 may be used toselectively couple the electrodes 10 a and 10 b to the controllablecurrent/voltage source 25 or the electronics 40. The electrodes 10 a and10 b may be coupled to the electronics 40, such as an amplifier andtelemetry system, when used to measure and record signals, for example.As illustrated, the switch 20 also enables selective coupling of one ormore of the electrodes 10 a and 10 b to one or more of the counterelectrodes 15 a and 15 b, for example, when desired to condition theelectrodes 10 a and 10 b to restore performance or create an AgCl layeron the surface thereof. In some embodiments, the switch 20 may couplethe controllable current/voltage source 25 to both of the electrodes 10a and 10 b. It should be understood, however, that when coupled to theelectrodes 10 a and 10 b, formation of material (e.g., AgCl) at thesurface of one of the electrodes 10 a or 10 b would necessarily resultin removal of material at the other one of the electrodes 10 a or 10 b.Accordingly, the counter electrodes 15 a and 15 b may be coupled to oneof the electrodes 10 a and 10 b so that conditioning of one of theelectrodes 10 a and 10 b can occur without hampering the performance ofthe other one of the electrodes 10 a and 10 b. For example, the switch20 may be used to couple one of the electrodes 10 a and 10 b in a pairwith one of the counter electrodes 15 a and 15 b (e.g., electrode pair10 a and 15 a, electrode pair 10 a and 15 b, electrode pair 10 b and 15a, or electrode pair 10 b and 15 b). In some embodiments, the switch 20may be used to couple each of the counter electrodes 15 a and 15 b to acorresponding one of the electrodes 10 a and 10 b, forming two electrodepairs (e.g. electrode pair 10 a and 15 a/electrode pair 10 b and 15 b orelectrode pair 10 a and 15 b/electrode pair 10 b and 15 a). In thismanner, each of the electrodes 10 a and 10 b can be individuallyreconditioned to optimize performance.

The controllable current/voltage source 25 may be configured to generateconditioning signals in accordance with embodiments of the presentinvention. As used herein, the term “conditioning signal” refers to anelectrical signal, such as an alternating current or direct currentsignal, that facilitates an electrochemical reaction at electrodes(e.g., electrodes 10 a and 10 b or counter electrodes 15 a and 15 b) towhich the controllable current/voltage source 25 is coupled. Theconditioning signal may be designed with a particular current, voltage,signal shape, and/or content to facilitate the desired electrochemicalreaction at the electrodes 10 a and 10 b, for example. Examples ofsuitable devices that can be used as the controllable current/voltagesource 25 include a wide variety of devices capable of generating thedesired conditioning signals, including batteries, simple power unitsfor generating electric energy, and signal generators, among others. Itshould be understood that the design and strength of the conditioningsignal may vary dependent upon a number of factors, including desiredconditioning (e.g., light reconditioning, heavy biofouling cleaning,total electrode surface regeneration, etc.) and electrode connectionscheme. For example, the conditioning signal may be a high-frequency,switching signal in which a layer of material (e.g., AgCl) may be formedon the surface of each of the electrodes 10 a and 10 b when a minorcleaning is desired. In some embodiments, the conditioning signal may bea direct current signal with a constant current. For example, a constantcurrent may be applied to each of the electrodes 10 a and 10 b of lessthan about 1 amp, less than about 500 milliamps, or less than about 200milliamps with a supply voltage of about 0.5 volts to about 5 volts and,alternatively about 2 volts to about 5 volts. In one embodiment, aconstant current of about 100 milliamps may be applied to each of theelectrodes 10 a and 10 b. In some embodiments, the conditioning signalmay have a varying voltage, for example, the conditioning signal maystart with a constant high voltage (e.g., about 5 volts to about 10volts) to induce formation of material on the electrode surface followedby a constant low voltage (e.g., about 2 volts to about 5 volts) onceformation has started.

One embodiment for using the conditioning system 5 for reconditioningelectrodes 10 a and 10 b will now be described. In accordance withpresent embodiments, the electrodes 10 a and 10 b may be deployed in thesea with a marine electromagnetic survey system. While deployed, theelectrodes 10 a and 10 b may be used, for example, to sense a parameter(e.g., voltages) than can be used to infer certain properties ofsubsurface rock, such as structure, mineral composition. During thissensing step, the switch 20 may selectively couple the electrodes 10 aand 10 b to electronics 45, such as an amplifier, for example. Aspreviously mentioned, the electrode performance may deteriorate duringuse due to a number of factors, including the accumulations ofundesirable deposits on the electrode surface, among others. In someembodiments, electrode performance may deteriorate such that the noisegenerated by the electrodes 10 a and 10 b may be greater than amplifiernoise, for example. At a desired time, a conditioning step may beperformed to optimize performance of the electrodes 10 a and 10 b. Insome embodiments, the conditioning step may be performed when the noiselevel from the electrodes 10 a and 10 b may in the range of from about−130 db rel 1V/sqrt (Hz) to about −170 db rel 1V/sqrt (Hz). For example,the conditioning step may be performed when the noise level from theelectrodes 10 a and 10 b is equal to or exceeds about −130 db rel1V/sqrt (Hz). In some embodiments, the electrodes 10 a and 10 b may beconditioned such that the noise level after conditioning is less thanabout −130 db rel 1V/sqrt (Hz). For the conditioning step, the switchmay selectively couple the controllable current/voltage source 25 to afirst electrode pair comprising one of the electrodes 10 a and 10 b andone of the counter electrodes 15 a and 15 b and to a second electrodepair comprising the other one of the electrodes 10 a and 10 b and theother one of the counter electrodes 15 a and 15 b. As discussed above,other electrode connection schemes may also be employed in accordancewith embodiments of the present invention. With the controllablecurrent/voltage source 25 coupled to the first and second electrodepairs, the conditioning step further may including sending aconditioning signal to each electrode pair, the conditioning signalbeing configured to remove material (e.g., AgCl) on the surfaces of theelectrodes 10 a and 10 b, in some embodiments. In alternativeembodiments, the conditioning signal may be configured to form material(e.g., AgCl) on the surfaces of the electrodes 10 a and 10 b. Inalternative embodiments, a first conditioning signal may be sent to eachof the electrode pairs configured to remove material on the surfaces ofthe electrodes 10 a and 10 b, followed by a second conditioning signalconfigured to form material on the surfaces of the electrodes 10 a and10 b. After the cleaning step, the switch 20 may selectively couple theelectrodes 10 a and 10 b to electronics 45, and an additional sensingstep may be performed, in accordance with certain embodiments.Performance of the electrodes 10 a and 10 b can be optimized, forexample, by alternating cleaning steps with sensing steps duringdeployment of the marine electromagnetic survey system.

FIG. 2 illustrates of an electrode conditioning system 5 in accordancewith alternative embodiments of the present invention. In theillustrated embodiment, the electrode condition system 5 includes morethan two electrodes 10 a-10 f rather than a single pair of electrodes 10a and 10 b, as illustrated by FIG. 1. It should be noted that while sixdifferent electrodes 10 a-10 f are shown on FIG. 2 and a single pair ofelectrodes 10 a and 10 b are shown on FIG. 1, the number of suchelectrodes 10 is not a limitation on the scope of the invention. Otherconfiguration may include any number of electrodes 10 that may besuitable for a particular application. In the embodiment illustrated byFIG. 2, the switch 20 may be used to selectively couple the electrodes10 a-10 f to the controllable current/voltage source 25 or theelectronics 45. As illustrated, the switch 20 also enables selectivecoupling of one or more of the electrodes 10 a-10 f to one or more ofthe counter electrodes 15 a and 15 b, for example, when desired tocondition the electrodes 10 a-10 f to restore performance. While only assingle switch 20 is illustrated, it should be understood that more thanone switch 20 may be used in accordance with embodiments of the presentinvention.

As previously mentioned, embodiments of the present invention may beused for conditioning of electrodes 10 (e.g., electrodes 10 a and 10 bon FIG. 1 or electrodes 10 a-10 f on FIG. 2) while deployed in the seawith a marine electromagnetic survey system. For example, embodimentsmay be used to condition electrodes 10 that are installed on a towedsurvey cable. In alternative embodiments, the electrodes 10 may be at afixed location with respect to an energy source, which may include, forexample, attachment of the electrodes 10 on one or more cablespositioned on the water bottom or attachment of the electrodes 10 to oneor more subsurface acquisition nodes.

FIG. 3 illustrates a marine electromagnetic survey system 55 thatincludes electrodes 10 a-10 f installed on a survey cable 60 inaccordance with embodiments of the present invention. In the illustratedembodiment, the marine electromagnetic survey system 55 includes asurvey vessel 65 moving along the surface of a body of water 70, such asa lake or sea. The survey vessel 65 generally may include equipment,shown generally at 75 and collectively referred to herein as a“recording system.” The recording system 75 may include devices (noneshown separately) for determining geodetic position of the vessel 65(e.g., a global positioning system satellite receiver signal), detectingand making a time indexed record of signals generated by each ofelectromagnetic sensors 90, and actuating one or more energy sources 80(explained further below) at selected times. As illustrated, the surveyvessel 65 may tow the source cable 85 and the survey cable 60, whereinenergy sources 80 are disposed on source cable 85. Although only twoenergy sources 80 and a single survey cable 60 are shown, this is forillustrative purposes only. It should be understood that the marineelectromagnetic survey system 55 may include more or less energy sources80 and survey cables 60. For example, in some embodiments, eight or morelaterally spaced apart survey cables 60 may be towed by the surveyvessel 65, while in other embodiments, up to 26 laterally spaced apartsurvey cables 60 may be towed by the survey vessel 65. The energysources 80 may be any selectively actuable sources suitable forsubsurface electromagnetic surveying, such as one or moreelectromagnetic field transmitters. Without limitation, the energysources 80 may generate current that diffuses through the water 70 andinto rock formations 95 beneath the water bottom 100, thereby creatingan electric field. As illustrated, the energy sources 80 may be towedthrough the water 70 at different depths with respect to one another.

As illustrated, the electromagnetic sensors 90 may be disposed on thesurvey cable 60 at spaced apart locations. The electromagnetic sensors90 may include, without limitation, any of a variety of electromagneticfield sensors, such as electrodes, magnetic field sensors, ormagnetometers. The electromagnetic sensors 90 may generate responsesignals, such as electrical or optical signals, in response to detectingchanges in the electric field generated by the energy sources 80 due tointeraction of the electric field with the rock formations 95. While notillustrated, additional equipment may be coupled to the survey cable 60,including, for example, position control devices and sensors of varioustypes, such as depth sensors. In the illustrated embodiment, theelectromagnetic sensors 90 include electrodes 10 a-10 f, switches 20a-20 c, and electronics 45 a-45 c.

The survey cable 60 further may include counter electrodes 15 a and 15 band controllable current/voltage source 25. The positioning of thecounter electrodes 15 a and 15 b on the survey cable 60 is forillustrative purposes only, and the present invention is not limited toinclusion of the counter electrodes 15 a and 15 b on the same section ofthe survey cable 60 as the electrodes 10 a-10 f. By way of example, forone survey cable 60 as seen in FIG. 3 two or more counter electrodes 15and 15 b may be used with connections through the survey cable 60 to theelectrodes 10 a-10 f. As described above, one or more of the electrodes10 a-10 f may be selectively coupled to the controllable current/voltagesource 25 and/or one or more of the counter electrodes 15 a and 15 b,for example, when desired to condition the electrodes 10 a-10 f torestore performance. By way of example, the switch 20 a may be used toselectively couple electrode 10 a with the controllable current/voltagesource 25 and the counter electrode 15 a for a cleaning step, which mayinclude removal and/or formation of material on the surface of one ormore of the electrodes 10 a-10 f.

FIG. 4 illustrates a second marine electromagnetic survey system 105that includes electrodes 10 a and 10 b installed on subsurfaceacquisition nodes 110, in accordance with embodiments of the presentinvention. In the illustrated embodiment, the second marineelectromagnetic survey system 105 includes a survey vessel 65 that movesalong the surface of the body of water 70. The survey vessel 65generally may include a recording system 75. A submersible vehicle 115carrying an energy source 80 may be attached to the survey vessel 65 bycable 120. One or more subsurface acquisition nodes 110 may be locatedon the water bottom 100. Although the embodiment shown in FIG. 4 showstwo subsurface acquisition nodes 110 and one energy source 80, it is tobe understood that the number of such subsurface acquisition nodes 110and energy source 80 is not a limitation on the scope of the invention.Other configurations may include more or fewer subsurface acquisitionnodes 110 and energy sources 80. Each of the subsurface acquisitionnodes 110 may include a flotation device 125, a ballast weight (notillustrated,) and electromagnetic sensors 90. The electromagneticsensors 90 may generate response signals, such as electrical or opticalsignals, in response to detecting energy emitted from the energy source80 after the energy has interacted with rock formations 95 below thewater bottom 100. As illustrated, the electromagnetic sensors 90 mayinclude electrodes 10 a and 10 b and electronics 45. Each of thesubsurface acquisition nodes further may include counter electrodes 15 aand 15 b, switch 20, and controllable current/voltage source 25. Asdescribed above, for each of the subsurface acquisition nodes 110, oneor more of the electrodes 10 a and 10 b may be selectively coupled tothe controllable current/voltage source 25 and/or one or more of thecounter electrodes 15 a and 15 b, for example, when desired to conditionthe electrodes 10 a and 10 b to restore performance. By way of example,the switch 20 may be used to selectively couple the electrode 10 a withthe controllable current/voltage source 25 and the counter electrode 15a for a cleaning step, which may include removal and/or formation ofmaterial on the surface of one or more of the electrodes 10 a-10 f.

FIG. 5 illustrates a third marine electromagnetic survey system 130 thatincludes electrodes 10 a-10 f installed on one or more cables 135positioned on the water bottom (not illustrated), in accordance withembodiments of the present invention. In the illustrated embodiment, thethird marine electromagnetic survey system 130 includes a survey vessel65 that moves along the surface of the body of water 70. The surveyvessel 65 generally may include a recording system 75 and tow one ormore energy sources 80. As illustrated, electromagnetic sensors 90 maybe disposed at the water bottom (not illustrated) on one or more cables135. In the illustrated embodiment, the electromagnetic sensors 90include electrodes 10 a-10 f, switches 20 a-20 c, and electronics 45a-45 c. The electromagnetic sensors 90 may generate response signals,such as electrical or optical signals, in response to detecting energyemitted from the energy source 80 after the energy has interacted withrock formations (not illustrated) below the water bottom. The signalsgathered by the electromagnetic sensors 90 may be communicated along thecables 135 to recording buoy 140, which can be, for example,electrically coupled to the electromagnetic sensors 90 by lead-in lines145. Although the embodiment shown in FIG. 5 shows three cables 135 eachwith a respective lead-in line 145 all of which are coupled to the buoy140, it is to be understood that the number of such cables 135, lead-inlines 145, and buoy 140 is not a limitation on the scope of theinvention. Other configurations may include more or fewer cables 135,lead-in lines 145, and buoys 140. Each of the cables 135 further mayinclude counter electrodes 15 a and 15 b, and controllablecurrent/voltage source 25. As described above, one or more of theelectrodes 10 a-10 f may be selectively coupled to the controllablecurrent/voltage source 25 and/or one or more of the counter electrodes15 a and 15 b, for example, when desired to condition the electrodes 10a-10 f to restore performance. By way of example, the switch 20 a may beused to selectively couple electrode 10 a with the controllablecurrent/voltage source 25 and the counter electrode 15 a for a cleaningstep, which may include removal and/or formation of material on thesurface of one or more of the electrodes 10 a-10 f.

While the preceding description describe the use of the counterelectrodes 15 a and 15 b for use in conditioning of electrodes 10 a-10f, the counter electrodes 15 a and 15 may also be used to generate anelectric field in the body of water 70. This electric field may then bedetected with one or more of the electrodes 10 a-10 f. Withoutlimitation, this detected electric field may be used for purposes ofcalibration and resistance measurement.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. It is therefore evident that the particular illustrativeembodiments disclosed above may be altered or modified and all suchvariations are considered within the scope and spirit of the presentinvention. All numbers and ranges disclosed above may vary by someamount. Whenever a numerical range with a lower limit and an upper limitis disclosed, any number and any included range falling within the rangeare specifically disclosed. Moreover, the indefinite articles “a” or“an,” as used in the claims, are defined herein to mean one or more thanone of the element that it introduces. Also, the terms in the claimshave their plain, ordinary meaning unless otherwise explicitly andclearly defined by the patentee. If there is any conflict in the usagesof a word or term in this specification and one or more patent or otherdocuments that may be incorporated herein by reference, the definitionsthat are consistent with this specification should be adopted for thepurposes of understanding this invention.

What is claimed is:
 1. A method, comprising: deploying electromagneticsensor electrodes in seawater during a marine electromagnetic survey;coupling at least one of the electromagnetic sensor electrodes to acontrollable current or voltage source while the electromagnetic sensorelectrodes are deployed in the seawater, wherein the coupling at leastone of the electromagnetic sensor electrodes to a controllable currentor voltage source comprises: coupling at least of the electromagneticsensor electrodes to a controllable current or voltage source and afirst counter electrode, wherein the first counter electrode is not oneof the electromagnetic sensor electrodes; and coupling another one ofthe electromagnetic sensor electrodes to the controllable current orvoltage source and a second counter electrode, wherein the secondcounter electrode is not one of the electromagnetic sensors electrodes,while the electromagnetic sensor electrodes are deployed, and sending asecond conditioning signal from controllable current or voltage sourceto the one of the electromagnetic sensor electrodes coupled to thesecond counter electrode; and sending a first conditioning signal fromthe controllable current or voltage source to the at least one of theelectromagnetic sensor electrodes coupled to the controllable current orvoltage source, wherein the first conditioning signal is sent from thecontrollable current or voltage source to the at least one of theelectromagnetic sensor electrodes through one or more lines, wherein theone or more lines are coupled to the electromagnetic sensor electrodesand to the controllable current or voltage source.
 2. The method ofclaim 1, wherein the electromagnetic sensor electrodes compriseAg/AgCl-based electrodes.
 3. The method of claim 1, wherein theelectromagnetic sensor electrodes comprise Ag/AgCl-based electrodes andthe step of sending a first conditioning signal results in creation ofone or more metal chloride layers on the surface of the at least one ofthe electromagnetic sensor electrodes coupled to the controllablecurrent or voltage source.
 4. The method of claim 1, further comprising:emitting an electric field into the seawater using the first and secondcounter electrodes, and detecting the electric field with theelectromagnetic sensor electrodes.
 5. The method of claim 1, wherein thesending the first conditioning signal from the controllable current orvoltage source results in formation of metal chloride on a surface ofthe at least one of the electromagnetic sensor electrodes coupled to thecontrollable current/voltage source.
 6. The method of claim 1, whereinthe sending the first conditioning signal from the controllable currentor voltage source results in removal of material from a surface the atleast one of the electromagnetic sensor electrodes coupled to thecontrollable current/voltage source.
 7. The method of claim 6, furthercomprising sending a second conditioning signal from the controllablecurrent/voltage source to the at least one of the electromagnetic sensorelectrodes coupled to the controllable current or voltage source to formmetal chloride on the surface of the electrode after the removal of thematerial from the surface of the electromagnetic sensor electrode. 8.The method of claim 1, further comprising coupling the electromagneticsensor electrodes to electronics, after the sending the firstconditioning signal, and then sensing changes in an energy field usingthe electromagnetic sensor electrodes, wherein the energy field wasemitted from an energy source and then interacted with one or more rockformations below a water bottom.
 9. The method of claim 1, wherein theat least one of the electromagnetic sensor electrodes coupled to thecontrollable current/voltage source has a noise level that exceeds about−130 dB rel 1V/sqrt (Hz) prior to the step of sending the firstconditioning signal.
 10. The method of claim 1, further comprisingtowing a survey cable on which the electromagnetic sensor electrodes aredisposed.
 11. The method of claim 1, wherein the electromagnetic sensorelectrodes are attached to a cable disposed on a water bottom.
 12. Themethod of claim 1, wherein the electromagnetic sensor electrodes areattached to a subsurface acquisition node.
 13. A method, comprising:towing a survey cable in a body of seawater, wherein the survey cablecomprises electromagnetic sensors disposed at spaced apart locations onthe survey cable, counter electrodes disposed on the survey cable, and acontrollable current or voltage source disposed on the survey cable, andwherein each of the electromagnetic sensors comprises Ag/AgCl-basedelectrodes; emitting energy from an energy source such that the energyinteracts with one or more rock formations below a bottom of the body ofseawater; detecting an energy change in the electromagnetic sensorsafter the energy has interacted with the one or more rock formations;coupling at least one of the Ag/AgCl-based electrodes to thecontrollable current/voltage source and at least one of the counterelectrodes while towing the survey cable; and sending a firstconditioning signal from the controllable current/voltage source tocondition the at least one of the Ag/AgCl-based electrodes coupled tothe controllable current/voltage source, wherein the first conditioningsignal is sent from the controllable current/voltage source to the atleast one of the Ag/AgCl-based electrodes through one or more lines. 14.The method of claim 13, wherein the first conditioning signal results information of AgCl on the surface of the at least one of theAg/AgCl-based electrodes coupled to the controllable current or voltagesource.
 15. The method of claim 13, wherein the first conditioningsignal results in removal of material from the surface of the at leastone of the Ag/AgCl-based electrodes coupled to the controllablecurrent/voltage source.
 16. The method of claim 13, wherein the firstconditioning signal is an alternating current signal or a direct currentsignal.
 17. The method of claim 13, wherein the first conditioningsignal comprises a direct current signal at a constant current of lessthan about 1 amp and a supply voltage of about 0.5 volts to about 5volts.
 18. The method of claim 1, wherein the first conditioning signalis an alternating current signal or a direct current signal.
 19. Themethod of claim 1, wherein the first conditioning signal comprises adirect current signal at a constant current of less than about 1 amp anda supply voltage of about 0.5 volts to about 5 volts.
 20. A method,comprising: sensing one or more parameters with a pair ofelectromagnetic sensor electrodes while deployed in a body of water,wherein the pair of electromagnetic sensor electrodes are selectivelycoupled to sensor electronics and a controllable current or voltagesource by way of a switch; forming a first electrode pair by couplingthe controllable current/voltage source to one of the electromagneticsensor electrodes and a counter electrode; and sending a direct currentor alternating current signal to the first electrode pair through one ormore lines that couple the controllable current or voltage source to thefirst electrode pair to remove material from surfaces of the one of theelectromagnetic sensor electrodes in the first electrode pair.
 21. Themethod of claim 20, wherein the first conditioning signal comprises adirect current signal at a constant current of less than about 1 amp anda supply voltage of about 0.5 volts to about 5 volts.
 22. The method ofclaim 19, wherein a switch is used to selectively couple a pair ofelectrodes to the controllable current or voltage source whenconditioning the pair of electrodes and to electronics when measuringand recording signals.